A Wisconsin golf course owner has said he received death threats after he advertised nine holes of golf for $9.11 to mark the anniversary of the September 11 terrorist attacks.

Tumbledown Trails Golf Course near Madison advertised the special in the Wisconsin State Journal newspaper on Monday, saying it was intended to commemorate the 12th anniversary of the attacks that killed nearly 3,000 people.

The discount, which also included 18 holes for $19.11, was valid for the anniversary on Wednesday only.

News of the offer spread on social media and the golf course's Facebook page was overrun with negative comments.

Course owner and general manager Marc Watts said he received death threats and threats to burn down the family-operated public golf course.

An apology posted by Mr Watts on Facebook said: "We would first like to apologise to everyone that we have upset or feels we have disrespected in anyway. By no means did we mean to do this."

Image Caption:One World Trade Center has been built on the site

He added that anyone who booked a tee off time under the offer would receive the deal, but that the course would donate the difference between the special rate and the normal daily rate to the 9/11 Memorial.

"We hope that everyone will now see this as a positive as we really meant it to be," he said. "Again we do sincerely apologise for offending anyone and hope that you do accept our sincere apology."

Mr Watts said he considered closing the 20-year-old golf course on Wednesday because of safety concerns but decided to keep it open.

The sheriff's department sent a deputy to the course on Tuesday, and Mr Watts said another officer will be back on Wednesday.

"We're a little hurt by the fact that people are putting such a negative context on this," Mr Watts said. "I thought people would appreciate it."

Mr Watts said he began running the promotion two years ago, and until now it had been warmly received.

But this year, after the newspaper ad circulated on social media, Mr Watts said the club's phone has been ringing off the hook.

It is not the first time that promotions tied to 9/11 have drawn criticism.

Last year the Coeur d'Alene Casino Resort Hotel in Worley, Idaho, offered hotel rooms for $91.11 and a food voucher for $9.11 as a "Thank you to our heroes".

Two years ago New York Sports Club offered 9/11 first-responders cheap memberships, drawing outrage from some who were targeted for the discount who said it a shameless use of a national tragedy to make money.